The insulin-like growth factor family of peptides, binding proteins and receptors: their potential role in tissue regeneration

The role of acid-labile subunit (ALS) in the modulation of GH-IGF-I action

Acid-labile subunit (ALS) deficiency (ACLSD) constitutes the first monogenic defect involving a member of the Insulin-like Growth Factor (IGF) binding protein system. The lack of ALS completely disrupts the circulating IGF system. Autocrine/paracrine action of local produced IGF-I could explain the mild effect on growth. In the present work we have revised the more relevant clinical and biochemical consequences of complete ACLSD in 61 reported subjects from 31 families. Low birth weight and/or length, reduced head circumference, height between -2 and -3 SD, pubertal delay and insulin resistance are commonly observed. Partial ACLSD could be present in children initially labeled as idiopathic short stature, presenting low IGF-I levels, suggesting that one functional IGFALS allele is insufficient to stabilize ternary complexes. Dysfunction of the GH-IGF axis observed in ACLSD may eventually result in increased risk for type-2 diabetes and tumor progression. Consequently, long term surveillance is recommended in these patients.

Recombinant IGFBP-3 inhibits allergic lung inflammation, VEGF production, and vascular leak in a mouse model of asthma

BACKGROUND

Vascular endothelial growth factor (VEGF) plays a pro-inflammatory mediator as well as a vascular permeability factor in bronchial asthma. Insulin-like growth factor (IGF)-I is also involved in the inflammatory process associated with bronchial asthma and stimulates VEGF expression. The IGF-binding proteins (IGFBPs), especially IGFBP-3, display distinctive properties and can interfere with various biological processes.

METHODS

In this study, an ovalbumin (OVA)-induced murine model of allergic airway disease was used to investigate which mechanism is implicated in the preventive and therapeutic actions of IGFBP-3 administered exogenously on allergen-induced bronchial inflammation and airway hyper-responsiveness, in particular focusing on the regulation of VEGF expression.

RESULTS

Administration of recombinant human IGFBP-3 to OVA-inhaled mice substantially attenuated the increases in hypoxia-inducible factor (HIF)-α activity, IGF-I production, and VEGF protein levels in the lung. In addition, the blockade of IGF-I action decreased the OVA-induced VEGF expression, airway inflammation, and bronchial hyper-responsiveness. The administration of recombinant human IGFBP-3 or CBO-P11 also reduced significantly increases in inflammatory cells, airway hyper-responsiveness, levels of IL-4, IL-5, IL-13, and vascular permeability in the lung of OVA-inhaled mice. Moreover, when recombinant human IGFBP-3 was administered after the completion of OVA inhalation, these therapeutic effects of IGFBP-3 were also observed.

CONCLUSIONS

These results indicate that IGFBP-3 administered exogenously may attenuate antigen-induced airway inflammation and hyper-responsiveness through the modulation of vascular leakage and VEGF expression mediated by HIF-1α/HIF-2α signaling as well as IGF-I action in allergic airway disease of mice.

Association of metabolic syndrome with insulin-like growth factors among adults in the US

OBJECTIVE

To examine the association of insulin-like growth factors (IGFs) with metabolic syndrome in a nationally representative sample.

METHODS

We used data from the Third National Health and Nutrition Examination Survey. Analysis is based on participants who provided a fasting blood sample and were aged 20 years and older (n = 5,903). Participants were classified by a number of risk factors for metabolic syndrome and stratified by diabetes status.

RESULTS

Each of the components of metabolic syndrome (increased waist circumference, higher triglycerides, lower HDL cholesterol, higher blood pressure, higher fasting glucose and diabetes) was each associated with lower levels of IGF-I, IGF-BP3 and the Ratio IGF-I/IGF-BP3. Each of the metabolic syndrome components was also associated with higher levels of insulin. Participants with 3-5 components of metabolic syndrome had significantly lower IGF-I and higher IGF-BP3 levels compared to adults with 1-2 components or 0 components, after adjustment for potential confounders. Participants with diabetes had lower levels of IGF-I and IGF-BP3, and higher levels of insulin, regardless of the number of metabolic syndrome components.

CONCLUSION

These findings may prove useful to an understanding of the role of IGF-I in human disease, in particular its relation to metabolic syndrome, diabetes and potentially some cancers.

Does pregnancy-associated plasma protein A have a role in allergic rhinitis?

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A), also known as insulin-like growth factor binding protein 4 protease, is postulated to be a new inflammatory marker in various clinical situations such as cardiovascular events, dialysis, renal transplantation, and asthma. PAPP-A also is produced in high concentrations by trophoblasts during pregnancy.

METHODS

We evaluated PAPP-A levels in allergic rhinitis patients and compared these with levels in healthy subjects. Thirty-one newly diagnosed allergic rhinitis patients and 29 healthy controls were included in the study. Serum PAPP-A, IgE, urea, creatinine, aspartate aminotransferase, creatine kinase (CK), CK-MB isoenzyme, total cholesterol, and triglyceride levels were determined.

RESULTS

The serum PAPP-A level was significantly higher (p = 0.013) in the allergic rhinitis group (6.1 +/- 2.9 mU/L) than in the control group (4.5 +/- 1.7 mU/L). The PAPP-A level in patients with allergic rhinitis and asthma (6.1 +/- 2.3 mU/L) was not significantly different (p = 0.959) from that in patients with allergic rhinitis alone (6.1 +/- 3.3 mU/L). The serum PAPP-A level in allergic rhinitis patients who had turbinate hypertrophy (6.9 +/- 2.2 mU/L) had a tendency to be higher than that in patients who had no turbinate hypertrophy (5.5 +/- 3.2 mU/L); however, this difference was not statistically significant (p = 0.151).

CONCLUSION

Increased PAPP-A activity may be involved in the inflammation and tissue remodelling that occurs in allergic rhinitis.

Pregnancy-associated plasma protein A in dialysis patients

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A) was recently described as a new marker of cardiovascular events and of inflammation in uremic patients. The aim of this study was to determine levels of PAPP-A in chronic dialysis patients and its possible relationships with renal osteodystrophy.

METHODS

A total of 99 adult chronic hemodialysis patients, 14 peritoneal dialysis patients and 41 control subjects were included in the study. Serum PAPP-A, intact parathormone (iPTH), calcium, phosphorus and alkaline phosphatase (ALP) were measured. The correlations between PAPP-A and iPTH, calcium, phosphorus and ALP were determined.

RESULTS

PAPP-A levels were significantly higher in peritoneal dialysis [4.5 (3.2-6.7) mU/L, median (interquartile range)], and hemodialysis patients [4.7 (3.8-6.5) mU/L] in comparison to control subjects [3.4 (3.0-5.0) mU/L] (p<0.05). In hemodialysis patients, post-dialysis PAPP-A levels [6.2 (4.7-9.4) mU/L] were significantly higher than pre-dialysis levels [4.7 (3.8-6.5) mU/L] (p<0.05). There was a weak but statistically significant positive correlation between serum PAPP-A and iPTH (r=0.216; p=0.041) and ALP (r=0.205; p=0.044) in the hemodialysis group. Correlation between the duration of dialysis therapy and PAPP-A levels was also significant (r=0.267; p=0.008) in the hemodialysis group.

CONCLUSIONS

PAPP-A levels are elevated in acute coronary syndromes and are closely related to inflammation and oxidative stress. We conclude that PAPP-A levels are increased in dialysis patients and may reflect a greater degree of chronic inflammation than osteodystrophy in uremic patients.

Insulin-like growth factor binding protein-3 is a novel mediator of apoptosis in insulin-secreting cells

Insulin-like growth factor binding protein-3 (IGFBP-3) is emerging as a critical regulator of cell survival. There has been no study which directly examined the potential role for this major growth factor in the programmed cell death (apoptosis) of insulin-secreting cells. To determine whether IGFBP-3 mediates apoptosis in insulin-secreting cells, we performed a rigorous series of experiments with the rat insulinoma (RIN) cell line m5F and the hamster insulin-secreting tumor (HIT) T-15. Within 24 h exogenous IGFBP-3 induced significant DNA fragmentation in RIN and HIT cells, at doses ranging from 4.4 to 2000 ng/ml (P<0.05) without a classic dose-response relationship. DNA fragmentation induced by rhIGFBP-3 occurred in the presence of immunoglobulin to block the type 1 IGF receptor. As detected by flow cytometry for Annexin V exposure to the cell surface, rhIGFBP-3 treatment doubled the proportion of apoptotic HIT cells from 1.7 +/- 0.4% (serum-free control) to 3.4 +/- 0.2% (P<0.02), an effect completely reversed by co-treatment with 1000 ng/ml rhIGF-I. Immunofluorescent microscopy disclosed that pro-inflammatory Th1 cytokines increased intranuclear aggregation of endogenous IGFBP-3. Cytokine-induced DNA fragmentation was completely blocked by relatively brief pre-treatment with antisense IGFBP-3 phosphorothioate oligodeoxynucleotides. In conclusion, we have presented the first evidence that IGFBP-3 contributes to cytokine-mediated apoptosis in insulin-secreting cells.

Insulin and insulin-like growth factor-I cause vasorelaxation in human vessels in vitro

BACKGROUND

Insulin and insulin-like growth factor-I (IGF-I) are endogenous peptides with vasoactive activities.

OBJECTIVE

To evaluate the vasodilatory effects of insulin and IGF-I on human vessels taken from patients with and without noninsulin-dependent diabetes mellitus (NIDDM) and to elucidate their mechanisms of action.

METHODS

Vascular rings of human internal mammary artery (IMA) and saphenous vein harvested from 54 patients with and without NIDDM undergoing coronary bypass surgery were studied in vitro.

RESULTS

For samples from patients without NIDDM both insulin and IGF-I (10(-12)-10(-7) mol/l) evoked greater relaxation in IMA rings (30 +/- 4 and 29 +/- 6%, maximal relaxation +/- SEM, respectively) than they did in saphenous-vein rings (43 +/- 4 and 42 +/- 5%, respectively, P < 0.05 both for insulin and for IGF-I). Similar results were obtained with vessels from patients with NIDDM. Relaxation was not affected by the removal of the endothelium and by inhibition of the production of nitric oxide. However, the vascular relaxation caused by insulin and IGF-I was completely abolished by KCI, and was attenuated by the nonspecific potassium-channel blocker tetraethylammonium (for IMA rings, to 77 +/- 8 and 66 +/- 4% with insulin and IGF-I, respectively; for saphenous vein rings, 73 +/- 2 and 77 +/- 1% for insulin and IGF-I, respectively, P < 0.001).

CONCLUSIONS

Both insulin and IGF-I induced endothelial-independent, nitric oxide-independent vasorelaxation of rings from human IMA and saphenous veins, through a mechanism involving activation of potassium channels. This response remained intact in vessels from patients with NIDDM. This result supports the hypothesis that insulin and IGF-I play roles in the regulation of vascular tone in human vessels.

Growth regulation of prostatic stromal cells by prostate-specific antigen

BACKGROUND

Prostate-specific antigen (PSA) is a serine protease that can cleave insulin-like growth factor-binding protein-3 (IGFBP3), thereby decreasing its affinity for insulin-like growth factor-I (IGF-I). Dissociation of the IGF-I-IGFBP3 complex renders IGF-I available to bind to its receptor and stimulates cellular proliferation. We evaluated the potential for PSA to modulate the effects of IGF-I and IGFBP3 on the proliferation of human benign prostatic hyperplasia (BPH)-derived fibromuscular stromal cells in primary cultures.

METHODS

We cultured BPH-derived stromal cells for 48 hours in serum-free RPMI-1640 medium supplemented with 0.2% bovine serum albumin and studied the effects of IGF-I, IGFBP3, PSA, and ZnCl(2) at varying concentrations. Differences in cell growth between control and treated cultures were evaluated by use of Dunnett's test. Concentration-related trends were evaluated by linear regression of log-transformed concentrations of test reagents on BPH-derived stromal cell number responses. Statistical tests were two-sided.

RESULTS

We observed a concentration-dependent proliferative response of BPH-derived stromal cells to IGF-I. IGFBP3 inhibited this response in a concentration-dependent fashion. IGFBP3 alone had no effect on stromal cell proliferation. When stromal cells were incubated with PSA alone or with PSA, IGF-I, and IGFBP3, an increase in stromal cell numbers that was dependent on PSA concentration was evident in both instances. Zinc, an endogenous inhibitor of PSA enzymatic activity, was able to attenuate the stimulatory effect of PSA at intraprostatic physiologic concentrations.

CONCLUSIONS

These results are consistent with the idea that PSA can modulate in vitro interactions between IGF-I and IGFBP3 and suggest that PSA may play a role in the regulation of human prostatic fibromuscular cell growth.

Elevated levels of the IGF-binding protein protease MMP-1 in asthmatic airway smooth muscle

We have previously demonstrated that the asthma-associated proinflammatory eicosanoid leukotriene D4 (LTD4) is co-mitogenic with insulin-like growth factors (IGFs) in airway smooth-muscle (ASM) cells in vitro. This synergistic effect of LTD4 and IGF on ASM cell growth involves proteolysis of ASM-produced IGF binding proteins (IGFBPs), which are cell growth-inhibitory proteins. We also identified this IGFBP protease to be the matrix metalloproteinase-1 (MMP-1), and showed that this enzyme had a significant role in modulating IGF action in ASM cells. In the present study, we tested the hypothesis that ASM hyperplasia in vivo involves induction of MMP-1 leading to IGFBP proteolysis. We detected the presence of MMP-1 and measured its levels in human airway tissue sections prepared from nonasthmatic and asthmatic subjects. Six nonasthmatic and six asthmatic airway tissue samples were analyzed for immunoreactive MMP-1 through an immunohistochemical detection method. Both the bronchial and tracheal smooth-muscle cells from different regions of the same sample were examined and documented. The immunostaining for MMP-1 was significantly elevated in both the bronchial and tracheal smooth-muscle cells of the airway sections from asthmatic samples relative to that of the nonasthmatic samples. The differences in levels of MMP-1, IGFBP-2, IGFBP-3, and IGFBP proteolytic activity were quantified using densitometric analyses of the ASM tissue extracts that were separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The MMP-1 levels in the asthmatic airway tissue extracts were 12-fold higher than those found in control samples. In addition, IGFBP-2 and IGFBP-3, which we have previously demonstrated to be proteolytic substrates of MMP-1, were found to be cleaved in asthmatic airway tissue extracts. Furthermore, the asthmatic airway extracts contained IGFBP proteolytic activity that was shown by immunodepletion studies to be due to MMP-1. These observations demonstrate that MMP-1 may play a significant role in inducing ASM hyperplasia and airway obstruction in asthma by modulating the IGF axis.

Insulin and insulin-like growth factor-I cause coronary vasorelaxation in vitro

Insulin and insulin-like growth factor-I (IGF-I) may play a role in the modulation of coronary artery tone, yet there are few data regarding their vasoactive effects on the coronary vascular bed. We evaluated the vasorelaxation effects of insulin and IGF-I on porcine coronary epicardial vessels in vitro and elucidated possible mechanisms. Porcine epicardial arteries were contracted with 10(-7) mol/L endothelin-1 and relaxed with cumulative concentrations of either insulin or IGF-I (10(-12) to 10(-7) mol/L). The above experiments were repeated in vessels without endothelium. Vessels were also incubated with the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 10(-4) mol/L) with and without 10(-3.5) mol/L L-arginine, the potassium channel blocker tetraethylammonium (TEA; 10(-2) mol/L), and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ; 10(-5.5) mol/L); vessels were then contracted with endothelin-1 and relaxed with insulin or IGF-I. Insulin and IGF-I were also added after contraction with 60 mmol/L KCl. Insulin and IGF-I caused a similar decrease in coronary epicardial tension after contraction with endothelin-1 (relaxation of 28+/-4% [n=7] and 25+/-3% [n=8] with insulin and IGF-I, respectively; P<0.0001 for both peptides). Removal of the endothelium did not affect these responses. Incubation with L-NMMA, but not ODQ, attenuated the vasorelaxation response to insulin and IGF in vessels without endothelium. L-Arginine did not reverse this effect of L-NMMA. KCl and TEA attenuated the vasorelaxation effect of both insulin and IGF-I. Thus, both insulin and IGF-I caused non-endothelium-dependent coronary vasorelaxation in vitro, probably through a mechanism involving the activation of potassium channels. These findings suggest that insulin and IGF-I participate in the regulation of coronary vasomotor tone.

Growth hormone-stimulated insulin-like growth factor (IGF) I and IGF-binding protein-3 in liver cirrhosis

BACKGROUND/AIMS

The aim of this study was to evaluate the liver's potential to generate insulin-like growth factor (IGF) I and IGF-binding protein-3 (IGFBP-3), following stimulation by human recombinant growth hormone, as a possible marker for liver functional reserve in patients with liver cirrhosis.

METHODS

In a pilot study, 15 patients (mean age 56 years) with postnecrotic liver cirrhosis were divided into two groups according to disease severity (Child-Pugh score): Group 1 (n=8) with scores of 5-8 and Group 2 (n=7) with scores of 9-12. Five age-matched healthy subjects served as controls. Human recombinant growth hormone (0.06 mg/kg) was administered subcutaneously on 2 consecutive days. Serum levels of IGF-I and IGFBP-3 were measured before and up to 48 h after human recombinant growth hormone injection. Nutritional status was assessed by the creatinine-height index and was compared to lymphocyte count, body mass index, and muscle arm circumference.

RESULTS

Baseline IGF-I levels were significantly lower in patients with cirrhosis than in controls, while no differences were noted between the two patient groups. IGF-I levels increased significantly after rhGH administration to the healthy controls, to a lower degree in Group 1, while no change occurred in Group 2. IGF-I levels at 24 h and beyond correlated significantly with the nutritional status, the Child-Pugh score, and the basal levels of GH-binding protein and IGFBP-3. IGFBP-3 serum levels did not change after rhGH stimulation.

CONCLUSIONS

IGF-I generation after GH stimulation may provide a new dimension in the assessment of liver function and nutritional status in patients with liver cirrhosis.

Insulin-like growth factor binding protein (IGFBP) proteases: functional regulators of cell growth

The IGFBP proteases were first described in pregnancy serum as a proteolytic activity against IGFBP-3. Since then, IGFBP proteases have been described in many other clinical situations, in various body fluids, and have been shown to cleave IGFBP-2 to -6 with varying specificity. The molecular nature of some of these proteases is being unraveled and three classes of IGFBP proteases have been recognized. These include kallikreins, cathepsins and matrix metalloproteinases (MMPs). We utilized two cellular systems to demonstrate the significance of IGFBP proteases in cellular growth regulation. In primary cultures of prostatic cells, we have shown that prostate-specific antigen (PSA) has the ability to enhance IGF mitogenic action by reducing the effects of IGFBPs. Similar kallikreins such as gamma nerve growth factor (NGF) share this activity. Within the prostatic milieu, we have also demonstrated epithelial production of the acid-activated IGFBP protease, cathepsin D, and its secretion into seminal plasma, as well as the serum of patients with prostate malignancy. We have also identified MMPs in prostatic cells and fluids. Using cultured airway smooth muscle (ASM) cells, we have demonstrated the synergism between IGFs and inflammatory agents in mediating ASM cell proliferation. Examination of this phenomenon revealed that these agents (e.g. leukotriene D4 and interleukin1-beta) induce the secretion of an IGFBP protease which cleaves the IGFBPs secreted by ASM cells, allowing IGFs to stimulate proliferation. Using several methods, including immunoblotting and immunodepletion techniques, we have identified this protease as MMP-1. These two pathophysiological systems demonstrate the importance of IGFBP proteases as autocrine paracrine growth regulators. Furthermore, IGFBP proteases may be critical elements in malignant and benign proliferative diseases, including prostate cancer and the ASM hyperplasia of long-standing asthma.